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CompletedNCT04520659Updated Jul 20, 2026Results posted

Evaluating the Infectivity, Safety and Immunogenicity of a Recombinant Live-Attenuated Respiratory Syncytial Virus Vaccine, LID/ΔM2-2/1030s, in RSV-Seronegative Infants and Children 6 to 24 Months of Age

A Phase 1 interventional study of RSV LID/ΔM2-2/1030s and Placebo in RSV Infection, sponsored by National Institute of Allergy and Infectious Diseases (NIAID). Completed at 3 sites in United States. Open to participants aged 6 Months to 24 Months, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-07-20.

Sponsored by National Institute of Allergy and Infectious Diseases (NIAID) · Phase 1, Interventional, and Prevention

Phase
Phase 1
Study type
Interventional
Enrollment
81
Allocation
Randomized
Ages
6 Months to 24 Months
Sex
All
01

Study summary

The purpose of this study is to evaluate the infectivity, safety, and immunogenicity of a single dose of a recombinant, live-attenuated respiratory syncytial virus (RSV) vaccine, LID/ΔM2-2/1030s, in RSV-seronegative infants and children 6 to 24 months of age.

Read the detailed description

This study will evaluate the infectivity, safety, and immunogenicity of a single dose of a recombinant, live-attenuated respiratory syncytial virus (RSV) vaccine, LID/ΔM2-2/1030s, in RSV-seronegative infants and children 6 to 24 months of age.

Participants will be randomly assigned to one of two groups to receive a single dose of intranasal RSV LID/ΔM2-2/1030s vaccine or placebo at study entry (Day 0). Group 1 (intensive) and Group 2 (less intensive) will differ only in the frequency of study visits and nasal swab collections.

Participants will receive study product between April 1 and October 15, outside of the RSV season, and will remain on the study until they complete the post-RSV season visit between April 1 and April 30 in the calendar year following enrollment. Participants' total study duration is between 6 and 13 months, depending upon time of enrollment.

Participants will attend several study visits throughout the study, which may include blood collection, nasal swabs, and physical examinations. Some of these visits may be remote if a stay at home order is put in place after enrollment.

02

Conditions studied

  • RSV Infection
03

In context

Respiratory Syncytial Virus Infections

293 studies on the registry are indexed under Respiratory Syncytial Virus Infections; 45 are open to participants now.

This study's enrollment of 81 is close to the median of 90 across 213 interventional studies indexed under Respiratory Syncytial Virus Infections.

Browse Respiratory Syncytial Virus Infections studies →

Lead sponsor

National Institute of Allergy and Infectious Diseases (NIAID) is the lead sponsor of 2,401 studies on the registry; 179 are open to participants now.

Of its 396 completed or terminated interventional studies of FDA-regulated products, 294 (74%) have results posted.

Counted across the registry records on this site, refreshed daily.

04

Who can participate

Ages eligible
6 Months to 24 Months
Sexes eligible
All
Accepts healthy volunteers
Yes

Inclusion criteria

  • ≥ 6 months of age and \<25 months of age at the time of inoculation
  • Screening and pre-inoculation serum specimens for respiratory syncytial virus (RSV)-neutralizing antibody are obtained no more than 42 days prior to inoculation
  • Seronegative for RSV antibody, defined as serum RSV-neutralizing antibody titer \<1:40
  • In good health based on review of the medical record, history, and physical examination at the time of inoculation
  • Received routine immunizations appropriate for age based on the Advisory Committee on Immunization Practices (ACIP) Recommended Immunization Schedule for Children and Adolescents Aged 18 Years or Younger

  • Growing normally for age as demonstrated on a World Health Organization (WHO) growth chart, AND

    • If \< 1 year of age: has a current height and weight above the 5th percentile for age
    • If ≥ 1 year of age: has a current height and weight above the 3rd percentile for age
  • Expected to be available for the duration of the study
  • Parent/guardian is willing and able to provide written informed consent

Exclusion criteria

Exclusion Criteria:

  • ≤ 6 months of age and > 25 months of age at the time of inoculation
  • Born at less than 34 weeks gestation
  • Born at less than 37 weeks gestation, and at the date of inoculation less than 1 year of age
  • Maternal history of a positive HIV test before or during pregnancy
  • Evidence of chronic disease
  • Known or suspected infection or impairment of immunological functions
  • Bone marrow/solid organ transplant recipient
  • Major congenital malformations, including congenital cleft palate or cytogenetic abnormalities
  • Suspected or documented developmental disorder, delay, or other developmental problem
  • Cardiac abnormality requiring treatment
  • Lung disease or reactive airway disease
  • More than one episode of medically diagnosed wheezing in the first year of life
  • Wheezing episode or received bronchodilator therapy within the past 12 months
  • Wheezing episode or received bronchodilator therapy after the age of 12 months
  • Previous receipt of supplemental oxygen therapy in a home setting
  • Previous receipt of an investigational RSV vaccine
  • Previous receipt or planned administration of anti-RSV antibody product including ribavirin, RSV Ig, or RSV mAb
  • Previous receipt of immunoglobulin or any antibody products within the past 6 months
  • Previous receipt of any blood products within the past 6 months
  • Previous anaphylactic reaction
  • Previous vaccine-associated adverse reaction that was Grade 3 or above
  • Known hypersensitivity to any study product component
  • Member of a household that contains an infant who is less than 6 months of age at the date of inoculation through the 28th day after inoculation

  • Member of a household that, at the date of inoculation through the 28th day after inoculation, contains an immunocompromised individual including but not limited to:

    • a person who is HIV-infected
    • a person who has cancer and has received chemotherapy within the 12 months prior to enrollment
    • a person living with a solid organ or bone marrow transplant
  • Attends a daycare facility that does not separate children by age and contains an infant \<6 months of age at the date of inoculation through the 28th day after inoculation

  • Receipt of any of the following prior to enrollment:

    • inactivated influenza vaccine within 3 days prior, or
    • any other inactivated vaccine or live-attenuated rotavirus vaccine within the 14 days prior, or
    • any live vaccine, other than rotavirus vaccine, within the 28 days prior, or
    • another investigational vaccine or investigational drug within 28 days prior, or
    • salicylate (aspirin) or salicylate-containing products within the past 28 days

  • Scheduled administration of any of the following after planned inoculation

    • inactivated vaccine or live-attenuated rotavirus vaccine within the 14 days after, or
    • any live vaccine other than rotavirus in the 28 days after, or
    • another investigational vaccine or investigational drug in the 56 days after

  • Receipt of any of the following medications within 3 days of study enrollment:

    • systemic antibacterial, antiviral, antifungal, anti-parasitic, or antituberculous agents, whether for treatment or prophylaxis, or
    • intranasal medications, or
    • other prescription medications except the permitted concomitant medications listed below
  • Permitted concomitant medications (prescription or non-prescription) include nutritional supplements, medications for gastroesophageal reflux, eye drops, and topical medications, including (but not limited to) cutaneous (topical) steroids, topical antibiotics, and topical antifungal agents.

  • Any of the following events at the time of enrollment:

    • fever (temporal or rectal temperature of ≥100.4°F), or
    • upper respiratory signs or symptoms (rhinorrhea, cough, or pharyngitis) or
    • nasal congestion significant enough to interfere with successful inoculation, or
    • otitis media
    • contact with a person diagnosed with COVID-19 disease or active severe acute respiratory syndrome coronavirus 2 (SARS CoV-2) infection within the preceding 10 days
05

Study design

Phase
Phase 1
Primary purpose
Prevention
Allocation
Randomized
Intervention model
Parallel assignment
Masking
Quadruple (Participant, Care provider, Investigator, Outcomes assessor)
Enrollment
81 participants (actual)

Study arms

  • Experimental
    Group 1: RSV LID/ΔM2-2/1030s

    Participants will receive a single dose of RSV LID/ΔM2-2/1030s vaccine at study entry (Day 0).

    Biological: RSV LID/ΔM2-2/1030s

  • Placebo comparator
    Group 1: Placebo

    Participants will receive a single dose of placebo at study entry (Day 0).

    Biological: Placebo

  • Experimental
    Group 2: RSV LID/ΔM2-2/1030s

    Participants will receive a single dose of RSV LID/ΔM2-2/1030s vaccine at study entry (Day 0).

    Biological: RSV LID/ΔM2-2/1030s

  • Placebo comparator
    Group 2: Placebo

    Participants will receive a single dose of placebo at study entry (Day 0).

    Biological: Placebo

Interventions

  • BiologicalRSV LID/ΔM2-2/1030s

    10\^5 plaque-forming units (PFU); administered as nose drops

  • BiologicalPlacebo

    Administered as nose drops

06

What researchers measure

Primary outcomes

  1. Frequency of Grade 1 or Higher Solicited Adverse Events (AEs) by Grade

    Solicited adverse events include fever; otitis media; upper respiratory illness (URI); lower respiratory illness (LRI) and cough (without LRI) as defined in Appendix III of the protocol document. The number of participants who experienced solicited adverse events was presented. A participant was only counted once in each solicited AE category, and that is in the line corresponding to the highest grade adverse event they had in that category. These events were graded (Grade 1-mild to Grade 4-life-threatening) following protocol-defined grading system outlined in Table 16 and Table 17 in the protocol document. Details regarding LRIs will be noted in Primary Outcome Measure #2.

    Time frame: Measured through Day 28

  2. Frequency of Grade 2 or Higher Lower Respiratory Infections (LRI) by Grade

    LRI may include wheezing, pneumonia, laryngotracheobronchitis (croup), rhonchi and rales as defined in Appendix III of the protocol document. A participant was only counted once in each LRI category, and that is in the line corresponding to the highest grade adverse event they had in that category. These events were graded (Grade 1-mild to Grade 4-life-threatening) following protocol-defined grading system outlined in Table 16 and Table 17 in the protocol document.

    Time frame: Measured through Day 28

  3. Number of Participants With Unsolicited Adverse Events (AEs) by Grade of Severity

    Unsolicited adverse events were other events, not included in the solicited AEs. The number of participants who experienced unsolicited adverse events was presented.

    Time frame: Measured through Day 28

  4. Number of Participants Who Experienced Serious Adverse Events (SAEs)

    A Serious Adverse Event (SAE) is an AE, whether considered related to the study product or not, that: Results in death during the period of protocol-defined surveillance; Is life threatening: defined as an event in which the patient was at immediate risk of death at the time of the event; it does not refer to an event that hypothetically might have caused death were it more severe; Requires inpatient hospitalization (or prolongation of existing hospitalization): defined as at least an overnight stay in the hospital or emergency ward for treatment that would have been inappropriate if administered in the outpatient setting; Results in a persistent or significant disability/incapacity; Is a congenital anomaly or birth defect, OR Is an important medical event that may not be immediately life threatening or result in death or hospitalization but may jeopardize the patient or may require intervention to prevent one of the outcomes listed above.

    Time frame: Measured Day 0 through Day 56 after inoculation and During the RSV Surveillance Season (Date of seasonal pause in enrollment in year of inoculation through March 31)

  5. Percentage of Vaccinees With a ≥4-fold Rise in Serum RSV-neutralizing Antibody Titer

    Serum RSV-neutralizing antibody titers were assessed by 60% RSV-plaque reduction neutralization titer (RSV-PRNT) assay. Antibody responses were defined as a greater than or equal to 4-fold increase in titer in paired specimens, between pre-inoculation and post-inoculation time points.

    Time frame: Measured at Day 0 and Day 56

  6. Peak Titer of Vaccine Virus Shed by Reverse Transcription Polymerase Chain Reaction (RT-qPCR) (Group 1 Only)

    This is the mean of the highest value per participant of the titer of vaccine virus shed. It was measured by RT-qPCR. Group 1 participants only. Only participants who met the definition of infection with vaccine virus were included.

    Time frame: Measured at Days 5, 7, 10, 12 and additional illness visits between Days 0 and 28.

  7. Number of Vaccinees Infected With RSV Vaccine Virus in Group 1

    Defined as shedding vaccine virus, detected by RT-qPCR, and/or ≥4-fold rise in RSV-specific serum antibodies, detected by enzyme-linked immunosorbent assay (ELISA) against the RSV F protein and/or an RSV-PRNT from study entry to Study Day 56

    Time frame: Measured through Day 56

Secondary outcomes

  1. Frequency of RSV-medically Attended Acute Respiratory Illness (MAARI) by Grade in Vaccine and Placebo Recipients Who Experience Natural Infection With Wild Type RSV During the Subsequent RSV Season

    The number of participants who had RSV-associated, symptomatic, medically attended respiratory and febrile illness (MAARI) among those who had indicators of natural infection with wt RSV were presented. Natural infection with wt RSV during the RSV season surveillance was defined as having either RSV detected in nasal swabs collected during illness visits for MAARI events or a \> 2.5-fold rise in serum antibodies from pre- to post-RSV season in the absence of RSV-associated medical events. A participant was only counted once in each solicited AE category, and that is in the line corresponding to the highest grade adverse event they had in that category. These events were graded (Grade 1-mild to Grade 4-life-threatening) following protocol-defined grading system outlined in Table 16 and Table 17 in the protocol document.

    Time frame: Measured during RSV season (from date of seasonal pause in enrollment in the year of inoculation through March 31)

  2. Frequency of RSV-medically Attended Acute Lower Respiratory Illness (MAALRI) by Grade in Vaccine and Placebo Recipients Who Experience Natural Infection With Wild Type RSV During the Subsequent RSV Season

    The number of participants who had RSV-associated, symptomatic, medically attended acute lower respiratory illness (MAALRI) among those who had indicators of natural infection with wt RSV were presented. Natural infection with wt RSV during the RSV season surveillance was defined as having either RSV detected in nasal swabs collected during illness visits for MAALRI events or a ≥ 2.5-fold rise in serum antibodies from pre- to post-RSV season in the absence of RSV-associated medical events. A participant was only counted once in each LRI category, and that is in the line corresponding to the highest grade adverse event they had in that category. These events were graded (Grade 1-mild to Grade 4-life-threatening) following protocol-defined grading system outlined in Table 16 and Table 17 in the protocol document.

    Time frame: Measured during RSV season (from date of seasonal pause in enrollment in the year of inoculation through March 31)

  3. Percentage of Vaccinees With a ≥4-fold Rise in Serum RSV preF IgG and/or RSV postF IgG

    Serum RSV preF IgG titers and RSV postF IgG titers were assessed by an Enzyme-linked Immunosorbent Assay (ELISA). Antibody responses were defined as a ≥4-fold increase in titer in paired specimens, between pre-inoculation and post-inoculation time points.

    Time frame: Measured at Day 0 and Day 56

07

Results

Posted Aug 22, 2025

Participant flow

Participants were recruited from pediatric practices and clinics in the greater Baltimore, MD/Washington, DC, Rochester, NY and Nashville, TN areas based on referral by the primary care provider or the provider's staff; and through electronic patient portals using IRB-approved messages. These recruitment methods targeted age-appropriate children between February, 2022 and March, 2023. The first participant was enrolled on 3/16/22 and the last participant was enrolled on 5/10/23.

Acute Phase (Days 0-28)
Participant flow — Acute Phase (Days 0-28)
MilestoneGroup 1: RSV LID/ΔM2-2/1030sGroup 1: PlaceboGroup 2: RSV LID/ΔM2-2/1030sGroup 2: Placebo
Started1474020
Completed1474020
Not completed0000
RSV Surveillance Phase Oct. 16-March 31
Participant flow — RSV Surveillance Phase Oct. 16-March 31
MilestoneGroup 1: RSV LID/ΔM2-2/1030sGroup 1: PlaceboGroup 2: RSV LID/ΔM2-2/1030sGroup 2: Placebo
Started1474020
Completed1373920
Not completed1010
Withdrew: Withdrawal by subject1010

Outcome measures

PrimaryFrequency of Grade 1 or Higher Solicited Adverse Events (AEs) by Grade

Solicited adverse events include fever; otitis media; upper respiratory illness (URI); lower respiratory illness (LRI) and cough (without LRI) as defined in Appendix III of the protocol document. The number of participants who experienced solicited adverse events was presented. A participant was only counted once in each solicited AE category, and that is in the line corresponding to the highest grade adverse event they had in that category. These events were graded (Grade 1-mild to Grade 4-life-threatening) following protocol-defined grading system outlined in Table 16 and Table 17 in the protocol document. Details regarding LRIs will be noted in Primary Outcome Measure #2.

Time frame:
Measured through Day 28
Reported as:
Count of participants · Participants
Frequency of Grade 1 or Higher Solicited Adverse Events (AEs) by Grade
ParticipantsGroup 1: RSV LID/ΔM2-2/1030sGroup 1: PlaceboGroup 2: RSV LID/ΔM2-2/1030sGroup 2: PlaceboGroups 1 and 2 Combined: RSV LID/ΔM2-2/1030sGroups 1 and 2 Combined: Placebo
Fever — Did not have this AE14727114118
Fever — Grade 1007272
Fever — Grade 2004141
Fever — Grade 3001212
Fever — Grade 4000101
Upper Respiratory — Did not have this AE4413121716
Upper Respiratory — Grade 193234327
Upper Respiratory — Grade 2103141
Upper Respiratory — Grade 3000000
Upper Respiratory — Grade 4000000
Lower Respiratory Illness (LRI) with RSV shedding — Did not have this AE14738175224
Lower Respiratory Illness (LRI) with RSV shedding — Grade 1000000
Lower Respiratory Illness (LRI) with RSV shedding — Grade 2001010
Lower Respiratory Illness (LRI) with RSV shedding — Grade 3000000
Lower Respiratory Illness (LRI) with RSV shedding — Grade 4000000
LRI in the absence of RSV shedding — Did not have this AE14739175324
LRI in the absence of RSV shedding — Grade 1000000
LRI in the absence of RSV shedding — Grade 2000000
LRI in the absence of RSV shedding — Grade 3000000
LRI in the absence of RSV shedding — Grade 4000000
Cough without LRI — Did not have this AE11629154021
Cough without LRI — Grade 12081101
Cough without LRI — Grade 2112132
Cough without LRI — Grade 3000000
Cough without LRI — Grade 4000000
Otitis media — Did not have this AE14737165123
Otitis media — Grade 1000000
Otitis media — Grade 2002121
Otitis media — Grade 3000000
Otitis media — Grade 4000000
PrimaryFrequency of Grade 2 or Higher Lower Respiratory Infections (LRI) by Grade

LRI may include wheezing, pneumonia, laryngotracheobronchitis (croup), rhonchi and rales as defined in Appendix III of the protocol document. A participant was only counted once in each LRI category, and that is in the line corresponding to the highest grade adverse event they had in that category. These events were graded (Grade 1-mild to Grade 4-life-threatening) following protocol-defined grading system outlined in Table 16 and Table 17 in the protocol document.

Time frame:
Measured through Day 28
Reported as:
Count of participants · Participants
Frequency of Grade 2 or Higher Lower Respiratory Infections (LRI) by Grade
ParticipantsGroup 1: RSV LID/ΔM2-2/1030sGroup 1: PlaceboGroup 2: RSV LID/ΔM2-2/1030sGroup 2: PlaceboGroups 1 and 2 Combined: RSV LID/ΔM2-2/1030sGroups 1 and 2 Combined: Placebo
Wheezing — Did not have this LRI14739175324
Wheezing — Grade 1000000
Wheezing — Grade 2000000
Wheezing — Grade 3000000
Wheezing — Grade 4000000
Pneumonia — Did not have this LRI14739175324
Pneumonia — Grade 1000000
Pneumonia — Grade 2000000
Pneumonia — Grade 3000000
Pneumonia — Grade 4000000
Laryngotracheobronchitis (Croup) — Did not have this LRI14738175224
Laryngotracheobronchitis (Croup) — Grade 1000000
Laryngotracheobronchitis (Croup) — Grade 2001010
Laryngotracheobronchitis (Croup) — Grade 3000000
Laryngotracheobronchitis (Croup) — Grade 4000000
Rhonchi — Did not have this LRI14739175324
Rhonchi — Grade 1000000
Rhonchi — Grade 2000000
Rhonchi — Grade 3000000
Rhonchi — Grade 4000000
Rales — Did not have this LRI14739175324
Rales — Grade 1000000
Rales — Grade 2000000
Rales — Grade 3000000
Rales — Grade 4000000
PrimaryNumber of Participants With Unsolicited Adverse Events (AEs) by Grade of Severity

Unsolicited adverse events were other events, not included in the solicited AEs. The number of participants who experienced unsolicited adverse events was presented.

Time frame:
Measured through Day 28
Reported as:
Count of participants · Participants
Number of Participants With Unsolicited Adverse Events (AEs) by Grade of Severity
ParticipantsGroup 1: RSV LID/ΔM2-2/1030sGroup 1: PlaceboGroup 2: RSV LID/ΔM2-2/1030sGroup 2: PlaceboGroups 1 and 2 Combined: RSV LID/ΔM2-2/1030sGroups 1 and 2 Combined: Placebo
Nasal Congestion — Did not have this14629164322
Nasal Congestion — Grade 101101102
Nasal Congestion — Grade 2000000
Nasal Congestion — Grade 3000000
Nasal Congestion — Grade 4000000
Emesis — Did not have this12736174824
Emesis — Grade 1103040
Emesis — Grade 2100010
Emesis — Grade 3000000
Emesis — Grade 4000000
Diarrhea — Did not have this13636164922
Diarrhea — Grade 1013132
Diarrhea — Grade 2100010
Diarrhea — Grade 3000000
Diarrhea — Grade 4000000
Conjunctivitis — Did not have this12739175124
Conjunctivitis — Grade 1100010
Conjunctivitis — Grade 2100010
Conjunctivitis — Grade 3000000
Conjunctivitis — Grade 4000000
Pain — Did not have this14639165322
Pain — Grade 1010102
Pain — Grade 2000000
Pain — Grade 3000000
Pain — Grade 4000000
Rash — Did not have this13738165123
Rash — Grade 1101121
Rash — Grade 2000000
Rash — Grade 3000000
Rash — Grade 4000000
Urinary tract infection — Did not have this14738175224
Urinary tract infection — Grade 1000000
Urinary tract infection — Grade 2001010
Urinary tract infection — Grade 3000000
Urinary tract infection — Grade 4000000
PrimaryNumber of Participants Who Experienced Serious Adverse Events (SAEs)

A Serious Adverse Event (SAE) is an AE, whether considered related to the study product or not, that: Results in death during the period of protocol-defined surveillance; Is life threatening: defined as an event in which the patient was at immediate risk of death at the time of the event; it does not refer to an event that hypothetically might have caused death were it more severe; Requires inpatient hospitalization (or prolongation of existing hospitalization): defined as at least an overnight stay in the hospital or emergency ward for treatment that would have been inappropriate if administered in the outpatient setting; Results in a persistent or significant disability/incapacity; Is a congenital anomaly or birth defect, OR Is an important medical event that may not be immediately life threatening or result in death or hospitalization but may jeopardize the patient or may require intervention to prevent one of the outcomes listed above.

Time frame:
Measured Day 0 through Day 56 after inoculation and During the RSV Surveillance Season (Date of seasonal pause in enrollment in year of inoculation through March 31)
Reported as:
Count of participants · Participants
Number of Participants Who Experienced Serious Adverse Events (SAEs)
ParticipantsGroup 1: RSV LID/ΔM2-2/1030sGroup 1: PlaceboGroup 2: RSV LID/ΔM2-2/1030sGroup 2: PlaceboGroups 1 and 2 Combined: RSV LID/ΔM2-2/1030sGroups 1 and 2 Combined: Placebo
Number of Participants Who Experienced Serious Adverse Events (SAEs)100010
PrimaryPercentage of Vaccinees With a ≥4-fold Rise in Serum RSV-neutralizing Antibody Titer

Serum RSV-neutralizing antibody titers were assessed by 60% RSV-plaque reduction neutralization titer (RSV-PRNT) assay. Antibody responses were defined as a greater than or equal to 4-fold increase in titer in paired specimens, between pre-inoculation and post-inoculation time points.

Time frame:
Measured at Day 0 and Day 56
Reported as:
Count of participants · Participants
Percentage of Vaccinees With a ≥4-fold Rise in Serum RSV-neutralizing Antibody Titer
ParticipantsGroup 1: RSV LID/ΔM2-2/1030sGroup 2: RSV LID/ΔM2-2/1030sGroups 1 and 2 Combined: RSV LID/ΔM2-2/1030s
Percentage of Vaccinees With a ≥4-fold Rise in Serum RSV-neutralizing Antibody Titer122537
PrimaryPeak Titer of Vaccine Virus Shed by Reverse Transcription Polymerase Chain Reaction (RT-qPCR) (Group 1 Only)

This is the mean of the highest value per participant of the titer of vaccine virus shed. It was measured by RT-qPCR. Group 1 participants only. Only participants who met the definition of infection with vaccine virus were included.

Time frame:
Measured at Days 5, 7, 10, 12 and additional illness visits between Days 0 and 28.
Reported as:
Mean · log 10 copies/mL
Peak Titer of Vaccine Virus Shed by Reverse Transcription Polymerase Chain Reaction (RT-qPCR) (Group 1 Only)
log 10 copies/mLGroup 1: RSV LID/ΔM2-2/1030sGroup 1: Placebo
Peak Titer of Vaccine Virus Shed by Reverse Transcription Polymerase Chain Reaction (RT-qPCR) (Group 1 Only)6.6 ± 1.3—
PrimaryNumber of Vaccinees Infected With RSV Vaccine Virus in Group 1

Defined as shedding vaccine virus, detected by RT-qPCR, and/or ≥4-fold rise in RSV-specific serum antibodies, detected by enzyme-linked immunosorbent assay (ELISA) against the RSV F protein and/or an RSV-PRNT from study entry to Study Day 56

Time frame:
Measured through Day 56
Reported as:
Count of participants · Participants
Number of Vaccinees Infected With RSV Vaccine Virus in Group 1
ParticipantsGroup 1: RSV LID/ΔM2-2/1030s
Number of Vaccinees Infected With RSV Vaccine Virus in Group 114
SecondaryFrequency of RSV-medically Attended Acute Respiratory Illness (MAARI) by Grade in Vaccine and Placebo Recipients Who Experience Natural Infection With Wild Type RSV During the Subsequent RSV Season

The number of participants who had RSV-associated, symptomatic, medically attended respiratory and febrile illness (MAARI) among those who had indicators of natural infection with wt RSV were presented. Natural infection with wt RSV during the RSV season surveillance was defined as having either RSV detected in nasal swabs collected during illness visits for MAARI events or a \> 2.5-fold rise in serum antibodies from pre- to post-RSV season in the absence of RSV-associated medical events. A participant was only counted once in each solicited AE category, and that is in the line corresponding to the highest grade adverse event they had in that category. These events were graded (Grade 1-mild to Grade 4-life-threatening) following protocol-defined grading system outlined in Table 16 and Table 17 in the protocol document.

Time frame:
Measured during RSV season (from date of seasonal pause in enrollment in the year of inoculation through March 31)
Reported as:
Count of participants · Participants
Frequency of RSV-medically Attended Acute Respiratory Illness (MAARI) by Grade in Vaccine and Placebo Recipients Who Experience Natural Infection With Wild Type RSV During the Subsequent RSV Season
ParticipantsGroup 1: RSV LID/ΔM2-2/1030sGroup 1: PlaceboGroup 2: RSV LID/ΔM2-2/1030sGroup 2: PlaceboGroups 1 and 2 Combined: RSV LID/ΔM2-2/1030sGroups 1 and 2 Combined: Placebo
Fever — Did not have this MAARI52116168
Fever — Grade 1003131
Fever — Grade 2002222
Fever — Grade 3413172
Fever — Grade 4000000
Upper Respiratory Illness — Did not have this MAARI4183124
Upper Respiratory Illness — Grade 1000202
Upper Respiratory Illness — Grade 252115167
Upper Respiratory Illness — Grade 3000000
Upper Respiratory Illness — Grade 4000000
Lower Respiratory Illness with RSV — Did not have this MAARI731892512
Lower Respiratory Illness with RSV — Grade 1000000
Lower Respiratory Illness with RSV — Grade 2101121
Lower Respiratory Illness with RSV — Grade 3100010
Lower Respiratory Illness with RSV — Grade 4000000
LRI in the absence of RSV — Did not have this MAARI8318102613
LRI in the absence of RSV — Grade 1000000
LRI in the absence of RSV — Grade 2101020
LRI in the absence of RSV — Grade 3000000
LRI in the absence of RSV — Grade 4000000
Cough without LRI — Did not have this MAARI6294156
Cough without LRI — Grade 1000101
Cough without LRI — Grade 231105136
Cough without LRI — Grade 3000000
Cough without LRI — Grade 4000000
Otitis media — Did not have this MAARI531271710
Otitis media — Grade 1000000
Otitis media — Grade 24073113
Otitis media — Grade 3000000
Otitis media — Grade 4000000
SecondaryFrequency of RSV-medically Attended Acute Lower Respiratory Illness (MAALRI) by Grade in Vaccine and Placebo Recipients Who Experience Natural Infection With Wild Type RSV During the Subsequent RSV Season

The number of participants who had RSV-associated, symptomatic, medically attended acute lower respiratory illness (MAALRI) among those who had indicators of natural infection with wt RSV were presented. Natural infection with wt RSV during the RSV season surveillance was defined as having either RSV detected in nasal swabs collected during illness visits for MAALRI events or a ≥ 2.5-fold rise in serum antibodies from pre- to post-RSV season in the absence of RSV-associated medical events. A participant was only counted once in each LRI category, and that is in the line corresponding to the highest grade adverse event they had in that category. These events were graded (Grade 1-mild to Grade 4-life-threatening) following protocol-defined grading system outlined in Table 16 and Table 17 in the protocol document.

Time frame:
Measured during RSV season (from date of seasonal pause in enrollment in the year of inoculation through March 31)
Reported as:
Count of participants · Participants
Frequency of RSV-medically Attended Acute Lower Respiratory Illness (MAALRI) by Grade in Vaccine and Placebo Recipients Who Experience Natural Infection With Wild Type RSV During the Subsequent RSV Season
ParticipantsGroup 1: RSV LID/ΔM2-2/1030sGroup 1: PlaceboGroup 2: RSV LID/ΔM2-2/1030sGroup 2: PlaceboGroups 1 and 2 Combined: RSV LID/ΔM2-2/1030sGroups 1 and 2 Combined: Placebo
Wheezing — Did not have this MAALRI8318102613
Wheezing — Grade 1000000
Wheezing — Grade 2001010
Wheezing — Grade 3100010
Wheezing — Grade 4000000
Pneumonia — Did not have this MAALRI8318102613
Pneumonia — Grade 1000000
Pneumonia — Grade 2101020
Pneumonia — Grade 3000000
Pneumonia — Grade 4000000
Bronchitis — Did not have this MAALRI8319102713
Bronchitis — Grade 1000000
Bronchitis — Grade 2100010
Bronchitis — Grade 3000000
Bronchitis — Grade 4000000
laryngotracheobronchitis (Croup) — Did not have this MAALRI8319102713
laryngotracheobronchitis (Croup) — Grade 1000000
laryngotracheobronchitis (Croup) — Grade 2100010
laryngotracheobronchitis (Croup) — Grade 3000000
laryngotracheobronchitis (Croup) — Grade 4000000
Rhonchi — Did not have this MAALRI9319102813
Rhonchi — Grade 1000000
Rhonchi — Grade 2000000
Rhonchi — Grade 3000000
Rhonchi — Grade 4000000
Rales — Did not have this MAALRI9318102713
Rales — Grade 1000000
Rales — Grade 2001010
Rales — Grade 3000000
Rales — Grade 4000000
Bronchiolitis — Did not have this MAALRI931992812
Bronchiolitis — Grade 1000000
Bronchiolitis — Grade 2000101
Bronchiolitis — Grade 3000000
Bronchiolitis — Grade 4000000
SecondaryPercentage of Vaccinees With a ≥4-fold Rise in Serum RSV preF IgG and/or RSV postF IgG

Serum RSV preF IgG titers and RSV postF IgG titers were assessed by an Enzyme-linked Immunosorbent Assay (ELISA). Antibody responses were defined as a ≥4-fold increase in titer in paired specimens, between pre-inoculation and post-inoculation time points.

Time frame:
Measured at Day 0 and Day 56
Reported as:
Count of participants · Participants
Percentage of Vaccinees With a ≥4-fold Rise in Serum RSV preF IgG and/or RSV postF IgG
ParticipantsGroup 1: RSV LID/ΔM2-2/1030sGroup 2: RSV LID/ΔM2-2/1030sGroups 1 and 2 Combined: RSV LID/ΔM2-2/1030s
RSV PreF IgG92130
RSV PostF IgG122739

Adverse events

Collected over From study entry to end of study. The duration of follow-up for a given participant was between 6 and 13 months for both Groups 1 & 2 depending on time of enrollment.. Non-serious events are listed at a 0% frequency threshold.

Adverse event summary by group
GroupDeathsSeriousOther
Group 1: RSV LID/ΔM2-2/1030s0/14 (0%)1/14 (7.1%)11/14 (78.6%)
Group 1: Placebo0/7 (0%)0/7 (0%)7/7 (100%)
Group 2: RSV LID/ΔM2-2/1030s0/39 (0%)0/39 (0%)31/39 (79.5%)
Group 2: Placebo0/18 (0%)0/18 (0%)13/18 (72.2%)
Groups 1 and 2 Combined: RSV LID/ΔM2-2/1030s0/53 (0%)1/53 (1.9%)42/53 (79.2%)
Groups 1 and 2 Combined: Placebo0/25 (0%)0/25 (0%)20/25 (80%)
Most frequent serious events
Most frequent serious events
EventGroup 1: RSV LID/ΔM2-2/1030sGroup 1: PlaceboGroup 2: RSV LID/ΔM2-2/1030sGroup 2: PlaceboGroups 1 and 2 Combined: RSV LID/ΔM2-2/1030sGroups 1 and 2 Combined: Placebo
WheezingRespiratory, thoracic and mediastinal disorders1/140/70/390/181/530/25
Most frequent other events
Showing 10 of 38
Most frequent other events
EventGroup 1: RSV LID/ΔM2-2/1030sGroup 1: PlaceboGroup 2: RSV LID/ΔM2-2/1030sGroup 2: PlaceboGroups 1 and 2 Combined: RSV LID/ΔM2-2/1030sGroups 1 and 2 Combined: Placebo
RhinorrheaRespiratory, thoracic and mediastinal disorders10/143/726/396/1836/539/25
RhinorrheaRespiratory, thoracic and mediastinal disorders6/145/718/399/1824/5314/25
CoughRespiratory, thoracic and mediastinal disorders5/144/718/398/1823/5312/25
FeverGeneral disorders5/143/714/396/1819/539/25
FeverGeneral disorders0/140/712/397/1812/537/25
Otitis mediaInfections and infestations5/142/713/395/1818/537/25
Nasal congestionRespiratory, thoracic and mediastinal disorders0/142/71/392/181/534/25
CoughRespiratory, thoracic and mediastinal disorders3/141/710/393/1813/534/25
Nasal congestionRespiratory, thoracic and mediastinal disorders0/141/710/392/1810/533/25
DiarrheaGastrointestinal disorders1/141/73/391/184/532/25

Baseline characteristics

Age, Customized
Age, Customized(Participants)Group 1: RSV LID/ΔM2-2/1030sGroup 1: PlaceboGroup 2: RSV LID/ΔM2-2/1030sGroup 2: PlaceboTotal
< 6 months of age00000
6-12 months of age8125842
13-18 months of age3210924
19-24 months of age345315
> 24 months of age00000
Sex: Female, Male
Sex: Female, Male(Participants)Group 1: RSV LID/ΔM2-2/1030sGroup 1: PlaceboGroup 2: RSV LID/ΔM2-2/1030sGroup 2: PlaceboTotal
Female10319941
Male44211140
Ethnicity (NIH/OMB)
Ethnicity (NIH/OMB)(Participants)Group 1: RSV LID/ΔM2-2/1030sGroup 1: PlaceboGroup 2: RSV LID/ΔM2-2/1030sGroup 2: PlaceboTotal
Hispanic or Latino206210
Not Hispanic or Latino127331870
Unknown or Not Reported00101
Race (NIH/OMB)
Race (NIH/OMB)(Participants)Group 1: RSV LID/ΔM2-2/1030sGroup 1: PlaceboGroup 2: RSV LID/ΔM2-2/1030sGroup 2: PlaceboTotal
American Indian or Alaska Native00000
Asian10113
Native Hawaiian or Other Pacific Islander00000
Black or African American10001
White117371873
More than one race10113
Unknown or Not Reported00101
Region of Enrollment
Region of Enrollment(participants)Group 1: RSV LID/ΔM2-2/1030sGroup 1: PlaceboGroup 2: RSV LID/ΔM2-2/1030sGroup 2: PlaceboTotal
United States147402081
08

Study locations

3 sites
  • John Hopkins Bloomberg School of Public Health
    Baltimore, Maryland 21205, United States
  • University of Rochester Medical Center
    Rochester, New York 14642, United States
  • Vanderbilt University
    Nashville, Tennessee 37232, United States
09

References and documents

Study documents

  • Protocol and statistical analysis plan · Feb 21, 2023
  • Informed consent form · Aug 31, 2021
  • Informed consent form · Aug 31, 2021

Documents are hosted by the registry — open the source record to download them.

Individual participant data

Plan to share: Yes — Qualified researchers may request access to IPD that underlie results in a publication. Patient level data will be anonymized and study documents will be redacted to protect the privacy of trial participants.

10

Updates

Tracking since Sep 25, 2026
No changes since tracking began. The registry record was last updated on Jul 20, 2026, before this site started recording changes on Sep 25, 2026. Its history is on ClinicalTrials.gov ↗
11

Registry details

Key details

Study ID
NCT04520659
Lead sponsor
National Institute of Allergy and Infectious Diseases (NIAID)
Collaborators
Sanofi Pasteur, a Sanofi Company
Responsible party
Sponsor
First posted
Aug 20, 2020
Start date
Mar 16, 2022
Primary completion
Apr 18, 2024
Completion
Apr 18, 2024
Results posted
Aug 22, 2025
Last update
Jul 20, 2026

Study contacts

Ruth A. Karron, MD
principal investigator · Johns Hopkins Bloomberg School of Public Health (JHSPH)

Oversight

Data monitoring committee
Yes
FDA-regulated drug
Yes
FDA-regulated device
No
View the source record on ClinicalTrials.gov ↗

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